It is well known that a remote unit's location within a wireless communication system may be determined using a trilateration method. According to such a method, distances between the remote unit and multiple base stations are calculated based on a measurement of time delay of a signal traveling between the remote unit and each base station. Such a prior-art method for calculating a remote unit's location is described in U.S. Pat. No. 5,508,708 "Method and Apparatus for Location Finding in a CDMA System" by Ghosh et al. and incorporated by reference herein. As described in U.S. Pat. No. 5,508,708, when location of a remote unit is desired, the uplink signal transmitted from the remote unit to multiple base stations is analyzed to determine propagation delay differences at each base station. From these propagation delay differences, a distance is calculated from each base station to the remote unit, and the location of the remote unit is determined.
Although prior-art methods of location can accurately determine the location of a remote unit, these methods are limited in that they are only capable of determining the location of remote units that are actively transmitting an uplink signal. In a commercial setting, where many remote units may be idle (i.e., monitoring a paging channel, but not actively transmitting an uplink signal), prior-art methods of location may be unavailable for a large population of remote units utilizing the communication system. Thus a need exists for a method and apparatus for remote unit location in a communication system that is capable of estimating the location of a remote unit not actively transmitting an uplink signal.